22 Memoirs o} the Indian Museum. [Vol. VIT, 



Subfamily PSEUDACANTHINAE. 



The most extensive genus of this subfamily, and one of the most primitive, appears to 

 be Popilius, a genus which, as limited by previous authors, has proved most difficult to define 

 satisfactorily. None of the characters hitherto used for this purpose appear really to have 

 more than specific value. Especially variable and untrustworthy, in many cases even as 

 a specific character, is the shape and size of the central tubercle. Some of the most definite 

 characters are found in the clypeus, but even these do not as a rule afford satisfactory 

 generic distinctions. It seems necessary, therefore, to sink the names Heliscus (—Soranus), 

 Odontotaenius (=Passalus, auct. nee Fabricius) and Passalotaenius as synonyms of Popilius. 

 Similarly Coniger, Rimor and Rimoricus may be sunk as synonym? of ileus. And 

 both Popilius and Oileus must be redefined. 



The plastic and primitive genus Popilius forms a starting point to which the remaining 

 genera of American Passalidae may be traced back, the more primitive species of all the 

 remaining subfamilies having the clypeus similarly exposed, although there is usually no 

 clypeofrontal suture, and the more highly specialized having it hidden. 



In the subfamily Pseudacanthinae itself three separate lines of evolution may be 

 recognized. In one, which includes a new genus Oileoides, and the genera Oileus and 

 Undulifer, the sides of the metasternum are broadly hairy. In another, which is represented 

 only by the genus Spurius, the central tubercle is absent. In the third the elytra are 

 united and the wings are of use for stridulation but not for flight. 



The more primitive members of the third group have the three terminal teeth of the 

 mandibles distinct as in Popilius. I have only seen three such species ; these belong to 

 the genera Pseudacanthus, Triaenurgus and Nasoproculus, in none of which are the sides of 

 the elytra hairy. It will be convenient to unite these three genera, and with them should 

 probably go the genera Ogyges, Prosoclitus and Truquius, which have hairless elytra — 

 unfortunately their mandibles have not been described. Petrejoides should perhaps come 

 here also, but Kuwert's definition is inconclusive, and I have nothing else to go by. The 

 name may equally well be synonymous with Proculejus or even with Proculej aides. 



The genera Proculejus} Prosoclitus, and Eriopterus should likewise, in all probability, 

 be united into one genus Proculejus, differing from Pseudacanthus in having only two teeth 

 at the apex of the mandible instead of three and in having hairy sided elytra. The 

 reduction in the number of teeth on the mandible probably takes place by the union 

 of the two lowest terminal teeth. The anterior lower tooth appears broad and bidentate in 

 this genus on both mandibles, instead of bidentate on the left and unidentate on the right as 

 in allied forms of the preceding genus. 



The genera of Pseudacanthinae may be defined thus : — 



The elytra separate, their vertical anterior part lightly concave .. .. 2. 



L \ The elytra united along the middle line, their vertical anterior 



part lightly convex . . . . . . . , . . . . 6. 



1 Except P. quitensis, Kaup (see below p. 51). 



